First version of smoke test on IE courtesy of saucelabs.com.

Using Node (and cofeescript) but only as a test dependency.
Use `npm install --dev; npm test` to run.

Very unpolished:
- **Tests mathdown.net instead of current source!**
- PASS/error results only appear to stdout.
- Likely to crash on test failure (without even freeing the browser, will timeout).
- Only tests IE.
- No option to test locally with PhantomJS which should be much faster.